1. Field of the Invention
This invention is directed generally to an improved part handling apparatus for use with an injection molding machine, and specifically to improvements in a preform retaining assembly used on an end-of-arm tool for handling and optionally conditioning preforms.
2. Background Information
The prior art relating to devices for handling preforms from an injection mold address the problems of preform production for the two-stage manufacture of finished blow molded articles. In a two-stage process, the preform production step is separated from the blow molding step by at least the necessity to substantially reheat the preform prior to blow molding. Therefore, the process for the production of preforms is typically optimized to minimize the production cycle time, and hence most prior art handling devices are designed to minimize the requirements for in-mold cooling. As a result, prior art handling devices provide solutions to improve heat transfer and to increase available cooling time. The most broadly used handling devices of the prior art uses an end-of-arm tool with an array of water cooled and vacuum assisted preform carrier tube assemblies. In addition, the tool may have a multiple (i.e. typically two or three) of tubes to injection mold stacks to lengthen the available cooling time. The typical prior art preform carrier tube assembly includes a tube with a closed end, and a tube insert. The tube 8 structure, as shown in FIG. 2C, is typically made from heat conductive Aluminum, and includes a molding surface that matches or slightly interferes with the preform 2 outer body geometry, and has an outside groove for circulating cooling water. The tube insert 9 is typically made from heat conductive Aluminum and includes molding surface that closely matches that of the preform end-portion geometry, and further provides a ported connection to a vacuum source. The molding surface of the tube 8 and tube insert 9 provide for conductive cooling of the preform as well as for preserving the preform geometry while it is still in a malleable state. A disadvantage of the water cooled part handling devices is in terms of the expense for circulating chilled water, higher maintenance costs due to corrosion, leaks, deposit build-up, as well as the added design and manufacture complexity.
As an alternative to two-stage, a single-stage process on an injection-blow molding system may be used. A single-stage process is distinct from two-stage in that it relies on the latent heat within a preform from the injection molding step to at least partially enable the blow molding of the finished article in a directly coupled blow molding step. The preforms produced in a single-stage process are typically transferred between the steps of injection and blow by a transfer device that is intended to minimize heat transfer from the preforms and to preserve their heat distribution. The prior art transfer devices for use in a single-stage process fall within categories of: circulation of the preform within its neck mold; mechanical gripper assemblies that engage a preform neck portion; and vacuum-assisted carrier tube assemblies. The prior art vacuum-assisted carrier tube, as shown in FIG. 3, is distinct from that of two-stage in that it lacks a cooling means and provides minimal molding surface, and thereby substantially addresses the requirement for minimal heat transfer. A problem with the prior art tube assembly has been a difficulty in attaining a reliably airtight seal between the preform end-portion 22 and the tube insert 9, the seal precluded by the combination of a rigid molding surface on the tube insert 9 and the variances in preform 2 geometry (i.e shrinkage, process variations). An improper seal allows for currents of air to swirl past the preform and into the insert port, the air currents may impart a cooling pattern of cold streaks wherever there has been contact between the air currents and the preform. The cold streaks effectively disrupt the required heat distribution in the preform and may negatively influence down-stream blow molding. Another problem with the prior art carrier tube, as shown in FIG. 3, is a high cost of manufacture due to a close-tolerance fit between the molding surface of the tube insert and the preform end portion.
In a single-stage process it is also necessary for a preform engaged in the transfer device to be maintained in a substantially fixed alignment such that the open end of the preform may be reliably aligned and engaged on a retaining device of the blow molding machine when being transferred. A problem with prior art carrier tubes has been a difficulty in providing sufficient alignment when transferring the preform onto the retaining device.
It is necessary for the production of many articles to present the preform to the blow mold in a particular angular orientation. For example, orientation of a preform for blow molding operations is frequently required when a thread on a blown bottle or the like must be accurately located in order to position a closure thereon. The angular orientation of a preform from the injection mold to the blow mold may be either preserved or regained. Regaining of the angular orientation as taught in prior art usually involves the interaction of a physical feature on the preform with a mechanism on the blow molding machine. For example, a pawl on a conveyor may interact with a lug feature on the preform to stop the rotation of the preform in a specific orientation. Regaining the angular orientation of a preform requires an extra step in the process, can be complicated and expensive, and may dictate the inclusion of an otherwise unwanted reference feature on the preform. In a two-stage process the angular orientation must be regained. In an injection-blow molding system operating a single stage process with circulating neck molds the angular orientation of the preform is inherently preserved. However, many injection-blow molding systems do not easily accommodate circulation of the neck molds and therefore is not a universally applicable solution. Therefore without resort to neck mold circulation, maintaining a known angular orientation of the preform from injection mold to blow mold requires that the preform not have any rotational freedom while engaged with either the transfer device or the retaining device of the blow molding machine. The maintenance of angular orientation while on the retaining device notwithstanding, the prior art vacuum carrier tubes do not adequately restrict the rotation of the preform during the part transfer from the injection mold and thereafter onto the retaining device, the rotational retention precluded by the lack of any substantial cohesion between the tube insert molding surface and the preform end-portion.
U.S. Pat. No. 5,447,426 to Gessner et al. describes an improved take-off plate device for removing molded articles from a molding machine and delivering them to a transfer or receiving station. The device includes a plate, one or more tubes mounted to the plate for receiving molded articles. Each of the tubes is provided with a cooling passageway for effecting cooling of the molded articles as they are moved between the molding machine and the receiving station. A bottom plug, which is in contact with the cooling passageway, is provided in each tube to more efficiently cool an end portion of the molded article in the tube. Preferably, the bottom plug has an end surface that matches the shape of the molded article end portion.
U.S. Pat. No. 6,186,736 to Lust et al. describes a method for removing and transporting articles from a mold. The teachings of the patent relate to the use of a part handling device that includes the use of resilient bellows-type end effectors for the vacuum handling of contact lenses as shown in FIG. 1. The part handling device does not provide any auxiliary means to align the part.
Co-pending United States application Ser. No. 09/982,994 to Vardin et. al describes a method and apparatus for transferring preforms in an injection-blow mol ding machine The injection-molding machine is capable of creating multiple groups of preforms during an injection cycle that are then transferred by group to an indexable table on the blow-molding machine through the use of an robotically actuated end-of-arm tool that includes preform carrier tubes. The preforms being held in carrier tubes by application of a vacuum in a known manner.
U.S. Pat. No. 5,902,612 to Ogihara describes an injection-blow molding apparatus which includes an apparatus to transfer the preforms from the injection molding machine to the blow molding machine by way of a first transfer to a simple rigid supporting member that includes a depression for receiving the bottom and part of the body of a preform, and a second transfer by an inverting mechanism that relies on engaging the neck portion of the preform.
U.S. Pat. No. 5,176,871 to Fukai describes a method and apparatus of forcibly cooling and solidifying preforms from interior and exterior thereof including the use of cooling tub es. A preform released from an injection mold is transferred therefrom retained within its neck mold, the preform inserted into the cooling tube until the preform comes close to a guide member, a cooling core is also inserted into the preform. The cooling tube having a bottom opening and an upper opening through which cooling airflows.
U.S. Pat. No. 5,282,526 to Gibbemeyer describes a method for orientating container preforms. The apparatus disclosed uses a plurality of pallets which support pairs of rotating mandrels for moving preforms, closed end down, to and through an orientation station. At the orientation station, the preforms are rotated with the mandrels, via individual rotary drive means, until an individual pawl engages a notch on each preform. Each pawl engagement is detected by a limit switch on each mandrel. Once all the pawls are engaged, a bumper is lowered by an actuator to engage a brake assembly which, when engaged, prevents further rotation of the mandrels. After the first pawl engages the first notch, a slip clutch is used which allows the drive motor to continue to rotate while associated drive elements stop. The actuator is then retracted to allow the pallets and mandrels to be released. This apparatus is complex and requires that the pallets be stopped at the orientation stations for the individual stations to orientate the preform. The necessity to stop the pallets for orientation presents problems in incorporating this design into continuous motion automated systems. Due to the individualized treatment necessary for orientating each preform on each pallet, the orientation station includes a complex arrangement of moving parts. Also, because orientation takes place at a stopped position, orientation is a lengthier process than it would be with continuous motion machines.
U.S. Pat. No. 6,059,557 to 1 ng et al. describes a cooling device to be used with an index molding machine. The cooling device includes cooling tubes for receiving and cooling at least one molded part, which cooling tubes are mounted to a surface of a carrier plate connected to the frame, and an actuation device for moving the carrier plate. The cooling device also includes at least one blowing tube for blowing cool air onto the at least one molded part.